Underground fuel storage tanks located at service stations and the like are filled with fuel, such as gasoline or diesel oil, through a fill pipe normally closed by a removable fill cap. Commercially available fill caps of this type comprise an over-center linkage arrangement which is adapted to actuate a plurality of latches for releasing the cap from its locked position on the pipe. In its locked position, a standard padlock is attached between the linkage and the cap proper to maintain the cap in its locked position on the fill pipe.
The security of conventional fill caps of this type is marginal since the padlock and/or linkage can be readily broken. For example, a standard crowbar can be used to break open the fill cap. In addition, when the fill cap includes a post arrangement to guide reciprocal movements of an actuating handle for the linkage, the linkage may prove difficult to operate as a result of the collection of dirt, snow or the like around the post.